Induced spawning in common sole ( Solea solea L.)

In Europe, the soles Solea solea (Linnaeus 1758) andSolea senegalensis (Kaup 1858) are considered amongthe most promising species for marine fish farming.Several studies conducted from the 1970s to developthe production technology of these species suggestedsimple schedules to obtain spontaneous spawning. Despitethese results and available technical information,nowadays, sole production is still at the pilotscale as breeders in captivity perform poorly or failto spawn.Moreover, for mass production essential knowledgeof some reproductive traits, such as ovulatoryperiod, spawn frequency, egg production and malefertility, is still scarce.With the aimof producing juveniles to supplementnatural recruitment, a broodstock of S. solea wasadapted to captivity and induced to reproduce. Thepresent study reports the results of 5 years of experiments.Sole breeders studied herein spontaneouslyspawned within the first year of captivity and eventuallyspawned inthe following year. However, in contrastto that reported by other authors, prolonged captivity apparently inhibited egg release.When egg release was inhibited in the stock tank,it always started inthe experimental groups just afteradministration of long-acting GnRHa yielding productionscomparable with spontaneous spawning,although concentrated in a shorter period.The effectiveness of long-acting GnRHa is furtherhighlighted by comparison with data on egg productionreported in the literature for soles spontaneouslyspawning (range 3000^240 000 embryos per kg BWper season) aswell as in short-acting LHRHa-induced females.Apart from hormonal treatment, other parameterssuch as diet andwater temperature are of paramountimportance in promoting proper gonadal developmentand spawning in captive soles